Noise-resistant two-wavelength interferometry for single-shot measurement of high-gradient flows

Abstract

This paper presents a new robust approach to measuring dynamic phenomena with high gradients using two-wavelength high-speed interferometry. A multiplexed interferogram with two different wavelengths and spatial-carrier frequencies is captured by a single high-speed camera shot. Quantitative processing of the interferogram is based on Fourier analysis, which is followed by a robust procedure to retrieve the unwrapped phase map with single-wavelength accuracy but with an extended range of unambiguity. This method is significantly more noise-resistant than the standard two-wavelength technique, which is sensitive to noise and synthetic phase distortion. The method was successfully applied to studying shock waves in a transonic compressor blade cascade in an industrial aerodynamic laboratory, where single-wavelength and standard two-wavelength approaches fail.